The agency raised the volcano alert level for Kuchinoerabu island, where Shindake is located, to 5, the highest on its scale. Shindake also erupted in August last year for the first time since 1980.

A military helicopter was sent to survey the island and assess damage. Chief government spokesman Yoshihide Suga told reporters in Tokyo that the coast guard had dispatched a ship to help evacuate the residents.

Nobuaki Hayashi, a local village chief, said about 120 of the island’s 137 residents were gathered at a local evacuation facility.

“There was a really loud ‘dong’ sound of an explosion, and then black smoke rose, darkening the sky,” he told national broadcaster NHK. “It smelled of sulfur.”

Hayashi said a few people on the island were still unaccounted for. One person, who lives in an area that is generally off limits, was to be evacuated by boat as he could not travel safely to the shelter by land.

“The skies here are blue, but smoke is still rising to the west,” he said.

ReutersKuchinoerabu is 80 kilometers (50 miles) southwest of the main southern island of Kyushu. A heavily forested, mountainous island bordered mostly by rocky cliffsides, it is a national park supported mainly by tourism and fishing.

Footage from NHK showed the mountain shrouded in light gray ash as the clouds from the eruption cleared.

Kuchinoerabu usually can be reached only by a once-a-day ferry from Yakushima island, 12 kilometers (7.5 miles) to the east, which has an airport and a population of more than 13,000 people.

Japan, which sits atop the Pacific “Ring of Fire,” has dozens of volcanoes and is frequently jolted by earthquakes.

In March 2011, a magnitude-9 earthquake rocked northeastern Japan, triggering a tsunami that killed more than 18,500 people and ravaged much of the northern Pacific coast.

Authorities recently closed part of a popular hot springs about 80 kilometers (50 miles) from Tokyo because of fears that Mount Hakone, which sits to the southeast of Mount Fuji, might erupt.

The eruption last September of another volcano, Mount Ontake in central Japan, killed 57 people.

Setsuya Nakada, a professor at Tokyo University, told NHK that the eruption on Kuchinoerabu was stronger than Mount Ontake’s.

Since the 2011 disasters, “this sort of activity has continued,” Nakada said, when asked if more eruptions were likely on the island. “Probably the eruptions will continue.”